Enthalpies of dissolution of long chain-length alkyltrimethylammonium bromide salts in water at temperatures from 278.15 to 308.15K

Riveros, D.C., Vargas, E.F. and Hefter, G.
(2015)
Enthalpies of dissolution of long chain-length alkyltrimethylammonium bromide salts in water at temperatures from 278.15 to 308.15K.
The Journal of Chemical Thermodynamics, 81
.
pp. 109-115.

Abstract

Molar enthalpies of dissolution, ΔslnHm, of decyl-, dodecyl-, tetradecyl- and hexadecyl-trimethylammonium bromide salts (RMe3NBr) in water have been measured calorimetrically as a function of concentration and temperature. Standard state values, ΔslnHm o, were obtained by extrapolation to infinite dilution and showed a smooth variation with the number of carbon atoms, nC, in the alkyl chain R, unlike their shorter congeners (nC ≤ 6). The corresponding molar isobaric heat capacity changes, ΔslnCp,m o, were calculated from the temperature dependence of ΔslnHm o and also varied smoothly with nC but were more than an order of magnitude greater than those of their shorter congeners, probably reflecting a marked increase in hydrophobicity with increasing nC. The behaviour of the RMe3NBr salts was found to parallel broadly that of the symmetrical tetraalkylammonium salts, R4NBr.